Device for volumetrically removing viscous liquids from vacuum operating equipments

ABSTRACT

A device for volumetrically removing liquids from vacuum operating equipments, particularly reaction vessels and equipments for obtaining polymers, comprising a set of mutually engaging pumping screws, a number of which extend to the inside of the vacuum equipment for a given length, while the remaining screw or screws extend only up to the bottom of said vacuum equipment. Said set of screws is rotatably driven within a body tightly enclosing the same.

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United States Patent [56] References Cited UNITED STATES PATENTS [72]Inventors FrancescoSiclari;

Luigi Marafioti; Franco Magnoni, all of e u u n yd r H u n 00 6 n n n 00w m m m G e hwmm H n nn n d enn O n Mee "IU- B SSZ M ..n 5245 ,m 44556fr. 99999 we HHHHHMiM 293 8 m l mw 74822 & 55868 Wm 4838 aim 38899 m wnnfl 22223 PAA a m s u m k a n .m I a N n 6 0 Mm V 8 1 .I 6 h 6 m u9 8 w9 mm-l 6 l -M 9 l I 8J2 A n s vmml n 2 m 9 .I M m ..lMm 0 06 N fi y mmin Dhwc m HM n AFPA P nflm nun 2247 333 [III III [54] DEVICE FORVOLUMETRICALLY REMOVING VISCOUS LIQUIDS FROM VACUUM OPERATING EQUIPMENTSABSTRACT: A device for volumetrically removing liquids from vacuumoperating equipments, particularly reaction vessels and equipments forobtaining polymers, comprising a set' of mutually engaging pumpingscrews, a number of which ex- 7 Claims, 5 Drawing Figs.

tend to the inside of the vacuum equipment for a given length, while theremaining screw or screws extend only up to the bottom of said vacuumequipment.'Said set of screws is rotatably driven within a body tightlyenclosing the same.

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SHEET 1 OF 2 A1 'Otxmye DEVICE FOR VOLUMETRICALLY REMOVING VISCOUSLIQUIDS FROM VACUUM OPERATING EQUIPMENTS BACKGROUND This inventionconcerns a device, essentially operating as a pumping means, forcontinuously and meteredly removing medium and high viscosity liquids,wherefrom gases and volatile fractions may be given off, from equipmentsand portions thereof wherein a subatmospheric pressure, or even a highvacuum is maintained. More particularly, the invention concerns a devicefor a continuous volumetric removal of the product from reaction vesselsand equipments wherein intermediate and final processes for obtainingpolymers, and in particular polyesters and polyamides, are carried out.

As well known, in the production and continuous processing of suchpolymerized materials, as well as during the completion of theirpolymerizing process within reaction vessels and equipments, wherein asubatmospheric pressure or even a high vacuum is usually maintained,difficulties are encountered in carrying out a continuous andvolumetrically metered removal of the related product. In fact,unfavorable physical properties, as e.g. a high viscosity and inparticular the ability to give off gaseous fractions, are shown by theproducts obtained from such intermediate and final processes. Saidviscosity may attain even very high values, of a few or even manyhundreds of Poises. Moreover, well defined thermal conditions should bemaintained, since a very narrowtemperature range is usually defined,below which the material cannot be kept in the required moltencondition, and above which decomposition phenomena occur.

The absence of pressure inside the environment wherefrom said viscousmaterials are to be removed and the remarkable drags encountered allalong the pipings through which said materials are conveyed to furtherprocessing equipments, require devices adapted to perform a highlyefficient pumping action for continuously removing said materials fromsaid equipments. Due to above reasons, said extraction devices are inthe form of different types of mechanical pumps, e. g. rotary pumps,gear pumps, screw pumps and the like.

Due to the abovestated and further reasons, such pumps operate underunfavorable conditions, particularly with respect to priming and to theability of uniformly removing the material, with a complete filling oftheir cavities and passages, In fact, it must be kept in mind that thematerial which shows a high viscosity and wherefrom gaseous fractionsare continuously evolved, is slightly forced to enter between thepumping elements. Sometimes the gravity force only, which anyway acts onthe ground of a very small head, operates to assist the introduction ofsaid material into the pump.

Amongst heretofore known pumping means, the multiple screw pumps oughttheoretically to ensure the most favorable results, owing to theirinherent regular and uniform outflow and to their good volumetricproperties. On the other hand, the multiple screw pumps, even whenengineered and operated according to the most advanced technicalstandards, show priming difficulties under the required conditions, arenot adapted to operate at rather high temperatures, and above all attemperatures wholly uniform in all points thereof, and cannot give highoutlet pressures.

SUMMARY An object of this invention is to provide a device for acontinuous volumetric removal of viscous fluids, wherefrom gaseousfractions are evolved, from equipments of the abovestated type and forthe considered applications, by which the drawbacks and operatingrestrictions of the heretofore known devices are obviated or at leastminimized.

More detailedly, this invention concerns a device for the stated orstrictly equivalent applications, comprising pumping means in the formof a system consisting of a plurality of cylindric screws, comparable tothe pumping system of pumps having multiple parallel screws, whichcounterrotate and mutually engage along their generatrices, such systembeing engineered, particularly in its inlet and priming part in such amanner as to ensure a complete filling of thread channels, before thethreads of the adjacent screws or screw get engaged thereinto.

A further object of the invention is to provide a multiple screw pumpingdevice showing the abovestated features, which is structurally andoperatively associated with the equipment wherefrom the product is to beremoved, in such a manner that said complete filling of thread channelscan occur directly inside the associated equipment, without anyintermediate passage wherein cavitation phenomena might occur andgaseous occlusions may be formed and maintained.

Another object of the invention is to provide a pumping device which inaddition to the abovestated features can ensure a substantially uniformtemperature of the removed material along the whole travel of saidmaterial therethrough.

According to the invention, the device is essentially characterized inthat it comprises a pumping system having a plurality of screws, andpreferably three cylindric and parallely fitted screws, mutuallyengaging all along their generatrices, the inlet section of saidmechanism being located inside the environment wherefrom said viscousliquid is to be removed and showing wide inlet ports radially directedtoward the screws, in front of which a number of screws is whollyexposed and uncovered, while the remaining screws start downstream ofsaid inlet port, in order to allow the viscous fluid to freely attainthe uncovered initial portions of the uncovered screws and to fill thespiral channels thereof across their whole development of 360 beforeengaging the thread of the other screw or screws thereinto.

A three screws pumping system comprising one driving central screwhaving a shaft extending to the outside of the device and connected todriving means, and two driven side screws, is preferably utilized. Theside screws extend to the inside of the equipment wherefrom the productis to be removed, while the driving screw extends essentially from thebottom wall of said equipment.

Moreover, the pumping device is preferably fitted within a tubularoutlet passage, which passes through a hollow space surrounding theenvironment and wherein a heating fluid is circulated, as already wellknown. Such an arrangement ensures a heating of the pumping systempractically all along its whole axial length. The device might comprisefurther jackets or heating means, extending to the outside of theequipment and fitted with pipe connections and inlet ports.

Sealing means, adapted to operate at relatively high temperature, e.g. astuffing box having ring-shaped packing glands made of asbestos or likefibers are preferably provided on the orifice through which the drivingshaft of the pumping mechanism extends to the outside.

DRAWINGS PREFERRED EMBODIMENT The embodiment of FIG. I shows a devicewhich is associated with-a polymerization reaction vessel or equivalentequipment, as eg a demonomerizing reactor, which in con sideredembodiment comprises an essentially vertical chamber. The casing 10 ofsaid chamber is wholly surrounded by a jacket I4, and through the thusdefined hollow space 13 a heating fluid, as e.g. diphenyl or the like,is circulated, as well known by those skilled in the art. The outletpassage of the equipment consists, as well known, ofa tubular duct 15,which inlet end defines the outlet port 16 of the casing 10, said ductbeing surrounded by the hollow space 13 and extending for a short lengthfrom said outlet port of the reactor chamber casing 10.

The above arrangement of the device is to be assumed as a notrestrictive example only, since the device according to the inventioncould be obviously associated, under conditions equivalent to theabovespecified ones, also with equipments of a different kind, e.g. withreaction vessels of the horizontal type, or reactors, demonomerizingvessels and other equipments, in case operated with screw feeders or thelike, provided that they show an outlet port located in the lowest pointof the processing environment, and wherein an amount 12 of the processedliquid to be remove-d is maintained to show a given head ll.

According to an already known technical solution, the device comprises atubuiar casing 20, wherein a hollow body 21 is fitted, said body 21being formed with seats for the screws, in particular a central screw 22and two symmetrically located side screws 23, which represent themovable com ponents of the pumping system.

The central screw 22 is rigidly connected with a hub 24 extending to theoutside, which is in turn secured to, or at any rate rotativelyconnected with, a shaft 25 which extends outwardly in such a manner thatits opposite end 26 can be connected, directly or through already knowntransmission means, with a suitable driving means (not shown).

As it can be seen in particular in FIGS. 1 and 2, the tubular casing 20of the pumping device extends for a given length into the processingchamber and is formed with a plurality of wide side windows 30, throughwhich the liquid to be removed can freely enter into said casing,essentially along the directions indicated by A in FIG. 1.

The plug 31 of the casing 20 is in turn formed with further orifices orpassages 32 (see FIGS. 2 and 3) to enhance said free access of liquidinto the casing.

The hollow body 21, wherein the pumping system is fitted, along with thecentral screw 22, terminate under the space wherein said passages orside windows are formed, whilst both side screws 23 extend upwardly intosaid space, the upper portions 23' thereof being thus wholly exposed andimmersed into the liquid filling the upper section of said casing 20.

The liquid flows into said space under the action of gravity. Due to thewidth of access passages, such flow is easily performed and moreover thevoiatile fractions which could be given off by the liquid, can be easilydischarged from said space, even when such phenomena occur directlyadjacent to the screws. In particular, the discharge of bubbles and gaspockets as formed by the evolution of volatiie fractions, is made easierthrough the upper orifices 32.

The liquid into said space will wholly fill the spiral channels of thewholly exposed upper sections 23' of the side screws, whereby it reachesthe area wherein the central screw engages both the side screws, in anamount exceeding the liquid which can be contained in said channelsafter the engagement thereof by the central screw. Thus, a cornpletevoiumetric filling of the pumping system and therefore a uniformlymetered removal are positively ensured. The pumping action is uniformlyexerted across the whole useful length of the screws, which issubstantially coincident with the screw por= tions extending through thelower protrusion of the heating hollow space 13, a good uniformity ofthe pumped liquid temperature being therefore ensured.

Further, exposed lengths 23" of the side screws 23 extend from the lowerend of the body 21 (see FIG. 1) into a discharge chamber 40, whilst thecentrai screw is connected to its extension 24 by a threadless core. Theremoved liquid is then fed from said discharge chamber to a deliveryduct 42, through an annular passage 43.

Also the walls defining said discharge chamber 40, as well as thepassage 41 and the duct 42, are advantageously fitted with jackets 41and 52 respectively, to allow a heating fluid to circulate throughsuitable pipe connections 53 and 54.

The casing 20 of the pumping device is preferably embodied in thestructure of the equipment, by rigidly securing a flange section 43,integral with the casing outer end, to a flange 44, that is on turnintegral with the equipment and in particular with the outer end of thetubular end part 15 thereof.

The rotary assembly is located by virtue of a component 45, that isformed e.g. with a flange 46, and whereon the central screw 22 issupported through suitable axial bearings of gaskets, while the sidescrews 23, which support pressure acts in an opposite direction, restagainst the upper plug or cap 31, e.g. through axially abutting buffers47 (see FIG. 2). The abutting surfaces of said thrust block systems aresimilarly or equally dimensioned, to ensure a good balance of workingconditions.

As shown in FIG. 1, the component 45 extends outwardly by means of atubular length 48, inside which a row of ringshaped packing glands 49,made e.g. of asbestos fibers is fitted, so to form a stuffing box thatcan be tightened by a stuffing nut 50.

Moreover a liquid buffer, which obviously shall neither react nor mixitself with the processed polymer, can advantageously be fed, e.g.through a duct 55, into the stuffing box, wherein it is kept under asuitable pressure, applied e.g. by means of nitrogen gas, and in caseaiso cooled.

However, since the device according to the invention has been describedand shown .as a not restrictive example only and merely to demonstrateessential features, it is to be understooci that the inventive idea canbe carried out in many different embodiment to better conform the sameto the different assembly and operational requirements, withoutdeparting from the true spirit and scope of the invention.

We claim:

1. A device for volumetrically removing viscous liquids from vacuumoperated equipments, particularly for the continuous production andprocessing of polymers, as e.g. polyesters and polyamides (intermediateand final reaction vessels for the polymerization and polycondensation,demonomerizers, finishers and the like), characterized in that itcomprises a pumping system having a plurality of parallely fittedcylindric screws, mutually engaging all along their generatrices andacting within a body tightly enclosing the same, a number of said screwsextending to the inside of the environment wherefrom the liquid is to beremoved, in such a manner as said number of screws be completely exposedto the liquid present in the environment, across their whole developmentof 360, while the remaining screw or screws, along with said body extendonly up to the bottom of said environment, whereby the thtead channelsof the exposed portions of said number of screws can be completelyfilled with the liquid before said channels get engaged with the threadsof said remaining screws.

2. A device according to claim 1, wherein the components of said pumpingsystem are fitted within a tubular casing, that in turn extends intosaid environment the extended casing length being formed with sidewindows or passages, to allow the liquid to fiow in a substantiallyradial direction, into the space wherein said uncovered screw portionslie.

3. A device according to claim 2, wherein said tubular casing is closedby a plug or cap means against which a number of screws are abutting,said plug or cap means being formed with windows or holes, particularlydesigned to allow a free exhaust in an upward direction of the volatilefractions that evolve from the liquid when entering into and between thepumping means.

4. A device according to ciaim 1, wherein the components of said pumpingsystem are located inside an outlet passage of said environment, whichextends through at least a part of a heating jacket associated to saidprocessing environment, the useful length of said mutually engagingscrews being enclosed in said outlet passage portion that extendsthrough said jacket.

system comprises a central screw, fitted coaxially to a driving 1 shaftand operatively connected therewith, said screw being directed andoperated in such a manner as to axially react in the outlet direction ofthe liquid, and formed with thrust resisting shoulders by which theouter structure of the device is acted upon; and two driven screwssymmetrically fitted on either sides of said central screw which extendupwardly and axially react on an upper plug or cap means provided insaid environment.

2. A device according to claim 1, wherein the components of said pumpingsystem are fitted within a tubular casing, that in turn extends intosaid environment the extended casing length being formed with sidewindows or passages, to allow the liquid to flow in a substantiallyradial direction, into the space wherein said uncovered screw portionslie.
 3. A device according to claim 2, wherein said tubular casing isclosed by a plug or cap means against which a number of screws areabutting, said plug or cap means being formed with windows or holes,particularly designed to allow a free exhaust in an upward direction ofthe volatile fractions that evolve from the liquid when entering intoand between the pumping means.
 4. A device according to claim 1, whereinthe components of said pumping system are located inside an outletpassage of said environment, which extends through at least a part of aheating jacket associated to said processing environment, the usefullength of said mutually engaging screws being enclosed in said outletpassage portion that extends through said jacket.
 5. A device accordingto claim 1, wherein the rotary components of said pumping system aredriven by a shaft that extends out of the pumping mechanism framethrough sealing means having heat resisting packings.
 6. A deviceaccording to claim 5, wherein said sealing means consist of a stuffingbox fitted with asbestos fiber packings, which can be saturated with aliquid buffer.
 7. A device according to claim 1, wherein said pumpingsystem comprises a central screw, fitted coaxially to a driving shaftand operatively connected therewith, said screw being directed andoperated in such a manner as to axially react in the outlet direction ofthe liquid, and formed with thrust resisting shoulders by which theouter structure of the device is acted upon; and two driven screwssymmetrically fitted on either sides of said central screw which extendupwardly and axially react on an upper plug or cap means provided insaid environment.